Bradley Manning faces up to 90 years in prison for leaking more than 700,000 diplomatic cables. Photograph: Patrick Semansky/AP

A military judge will on Wednesday announce the prison sentence for Bradley Manning, who gave reams of classified information to WikiLeaks.

Colonel Denise Lind said Tuesday she was still deliberating but she was confident she would have a sentence by Wednesday morning.

"At 10am tomorrow I will announce the sentence," she said. Lind made the statement about two and a half hours into her deliberations.

Manning faces up to 90 years in prison for leaking more than 700,000 Iraq and Afghanistan battlefield reports and State Department diplomatic cables in 2010 while working as an intelligence analyst in Iraq. He also leaked video of an US helicopter attack in Baghdad in which at least nine people were killed, including a Reuters news photographer and his driver.

Prosecutors have asked for at least a 60-year prison term. Captain Joe Morrow said in his closing argument Monday that a long prison sentence would dissuade other soldiers from following in Manning's footsteps.

"There's value in deterrence," Morrow said.

The defense has suggested a prison term of no more than 25 years, so that Manning could rebuild his life productively after his release. Defense attorney David Coombs asked for a sentence that "doesn't rob him of his youth."

Manning must serve at least one-third of any prison sentence before becoming eligible for parole. He will get credit for about three and a half years of pretrial confinement, including 112 days for being illegally punished by harsh conditions at the Quantico brig in Virginia.

Manning was convicted last month of 20 offenses, including six Espionage Act violations, five theft counts and computer fraud.

Under military law, the verdict and sentence must be reviewed — and may be reduced — by the commander of the military district of Washington, currently Major General Jeffery S Buchanan. If Buchanan approves a sentence that includes a bad-conduct discharge, a dishonorable discharge or confinement for a year or more, the case will be automatically reviewed by the army court of criminal appeals.

Further appeals can be made to the military's highest court, the US court of appeals for the armed forces, and the US supreme court.